1. Field of the Invention
The present invention relates to organic color pigment lakes, and, more especially, to organic pigment lakes comprised of a high molecular weight or polymeric dye reduced or diluted by a substratum or extender therefor.
2. Description of the Prior Art
A "lake" is defined by the U.S. Tariff Commission as a full strength toner or coloring agent reduced or diluted by an inert, insoluble, colorless, solid extender. The commonly used prior art substrate or extender is alumina, usually light alumina hydrate. The commercially available lakes are typically prepared by co-precipitation of an organic dye with a water-insoluble, inorganic substrate; again, usually an alumina hydrate carrier. Such materials include lakes made from Food, Drug and Cosmetic approved dyes (so-called FD&C lakes), Drug and Cosmetic approved dyes (D & C lakes), and other non-certified dyes. Typical prior art lakes include Acid Yellow 1, Lake, which is the monomeric dye, ##STR1## ON ALUMINA, Alizarine Lake, which is a calcium salt of the compound dihydroxyanthraquinone on alumina, and Peacock Blue Lake, also known as FD&C Blue 1 Alumina Lake and FD&C Blue 4, which is the alumina hydrate lake of the monomeric dye, Erioglaucine.
FD&C lakes are important to food processors who formulate non-aqueous or low moisture content products. Typical applications include: hard fat coatings, frosting sugars, icings and fondant coatings, cake and doughnut mixes, variegating sauces, dry beverage and dessert powders, snack foods, pet foods, and various tablet coatings for the confection and pharmaceutical industries. In addition, FD&C, and, in certain cases, D&C, lakes find use in cosmetics (lotions, creams, lipsticks, powders and soaps) and packaging materials for the food and pharmaceutical industries (inks, films, coatings and can liners).
The FD&C, D&C, and noncertified lakes find application outside these industries being employable in some pigment applications, such as in lithographic and printing inks, in artist colors, and in crayons.
Notwithstanding their present use, conventional lakes have several critical failings which limit their applicability. They generally bleed--that is, absorbed organic dye washes off the inorganic substrate in use. Also, even with lakes which exhibit small amounts of bleed at relatively neutral pH, such as from about pH 4 to pH 9, at alkaline or acidic conditions such as in strong base or acid, lakes discharge their color into a soluble form. Furthermore, the amount of dye which may be incorporated into conventional lakes is limited to about 20-40% by weight of the total lake composition. At higher dye loadings, excessive bleed is encountered. This low loading means that the desirable covering powder of pigments is often not possible to achieve with lakes. Moreover, conventional lakes are often excessively sensitive to attack and discoloration by light and chemical (such as reducing) agents.